Ferromagnets with two-dimensional (2D) van der Waals honeycomb structures are attracting a great deal of research interests in condensed matter physics thanks to their potential for dissipationless spintronic applications [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}. In these materials, chemically stable atomic layers are stacked on top of each other via weak van der Waals forces allowing relatively easy exfoliation of single monolayers. The intrinsic 2D ferromagnetism was first observed in Cr\(_2\) Ge\(_2\) Te\(_6\)  and CrI\(_3\)  where the Curie temperatures remain finite down to their monolayer limits [2]}, [3]}. These experimental results demonstrate that the magnetic anisotropy in these 2D materials are strong enough to overcome thermal fluctuations inherent in low-dimensional magnets [11]}, [12]}. In CrI\(_3\) , the interlayer exchange couplings between ferromagnetic layers were observed to change from ferromagnetic to antiferromagnetic as the number of stacked monolayers decreased [13]}, [14]}, [15]}, [16]}. Such remarkable behavior is ascribed to the changes in the mode of stacking, for instance, from rhombohedral to monoclinic. Similar stacking-dependent 2D orderings were soon observed also in isostructural CrBr\(_3\)  and CrCl\(_3\)  [4]}, [18]}, [19]}.
